The present invention relates to an image forming device, such as a digital copy machine, facsimile device, or scanner device, which performs resolution conversion processing or scaling processing of a binary image and outputs a processed image.
In image forming devices such as digital copy machines, facsimile devices, and scanner devices, inputted images of written characters, etc. often undergo enlargement processing, resolution conversion, etc.
Conventionally, when performing binary resolution conversion or scaling, the method generally used was simply to increase the number of or selectively skip pixels. The advantage of this method was that the necessary hardware could be easily realized.
Binary, i.e. one-bit image data was generally expressed as shown in FIG. 29(a), and when outputted by a hard copy device, etc., this data was outputted as shown in FIG. 29(b).
In order to simply magnify by two times, data was interpolated to obtain four times the data quantity of FIG. 29(b), yielding output data shown in FIG. 29(c). In the case shown in FIG. 29(c), the dot diameter of the hard copy device is reduced by half, and the dot density is increased by four times.
If, on the other hand, the dot diameter of the hard copy device is the same as that in FIG. 29(b), the image is outputted enlarged by two times. Accordingly, the dot diameter of the hard copy device determines whether resolution conversion or scaling is performed.
However, merely enlarging, etc., a binary image using this method gives rise to fixed patterns, stripes, etc. such as the display of edges of written characters, etc. as rough, stair-step shapes. Thus, from the point of view of the outputted image, this method produced very unattractive images.
For this reason, in order to display such rough edges more smoothly, processing called smoothing has recently been adopted. One example of smoothing is the enlarged character correction method disclosed in Japanese Unexamined Patent Publication No. 63-172:664/1988 (Tokukaisho 63-172664).
The foregoing conventional art is a method of enlarging a standard character pattern by two times vertically and horizontally. As shown in FIGS. 30(a) through 30(d), when a predetermined pattern of 3xc3x973 pixels is detected, a corresponding correction pattern is calculated using a certain computing formula.
However, the foregoing conventional correction method only enlarges two times vertically and horizontally, and is only able to detect small patterns of 3xc3x973 pixels. Thus inclined lines of shallow angle, for example, cannot be detected as other than horizontal lines, and smoothing correction cannot be performed over a wide extent.
It is an object of the present invention to provide a low cost image forming device capable of performing resolution conversion or scaling processing of high image quality, which enables smoothing correction of, in particular, inclined lines of shallow angle, such as gradually inclined images.
In order to attain the foregoing object, an image forming device according to the present invention includes an edge detecting section, which detects length and shape of an edge of a binary image; and an interpolating section, which, based on the length and shape of the edge detected by the edge detecting section, performs resolution conversion processing or scaling processing of the binary image.
With the foregoing structure, when forming an image by resolution conversion or scaling of a binary image, the edge detecting section detects the length and shape of the edge. An edge is an area of change from black to white pixels or from white to black pixels, and accordingly the length and shape of an edge can be grasped on a pixel-by-pixel basis. For this reason, the edge detecting section can detect the incline of a line of shallow angle.
Then, since the interpolating section performs resolution conversion processing or scaling processing on the basis of the length and shape of the edge detected by the edge detecting section, pixels can be interpolated at optimum positions.
As a result, it is possible to provide an image forming device of low cost, capable of performing resolution conversion or scaling processing of high image quality, which enables smoothing correction of, in particular, inclined lines of shallow angle, such as gradually inclined images.
In order to attain the foregoing object, an image forming device according to the present invention may also include an edge detecting section, which detects an edge of a binary image, and detects length and shape of the edge; an interpolating section, which, based on the length and shape of the edge detected by the edge detecting section, performs resolution conversion processing or scaling processing of the binary image; a pattern mask section, which performs resolution conversion processing or scaling processing by means of a pattern matching mask; and a combining section, which combines the resolution conversion processing or scaling processing performed by the interpolating section and the resolution conversion processing or scaling processing performed by the pattern mask section.
With the foregoing structure, the method of resolution conversion processing or scaling processing by detection of length and shape of an edge, performed by the edge detecting section and the interpolating section, is combined, by the combining section, with resolution conversion processing or scaling processing using a pattern matching mask, performed by the pattern mask section. Consequently, a wide range of resolution conversion rates or scaling rates can be used.
As a result, even finer edges can be made smooth.
Additional objects, features, and strengths of the present invention will be made clear by the description below. Further, the advantages of the present invention will be evident from the following explanation in reference to the drawings.